Stroke is the third leading cause of death and the leading cause of disability in the United States. Ischemic stroke is caused by a blockage of blood flow to one or more brain arteries, usually due to a blood clot. As a result there is a reduced supply of oxygen and other nutrients leading to permanent brain damage. Normobaric oxygen therapy (NBO, or high-flow oxygen delivered via a facemask) shows promise as a simple, widely accessible, low-cost therapy that can prevent stroke-related brain damage and extend the time window for administering the clot-busting drug t-PA (tissue plasminogen activator), which is the only acute stroke treatment approved by the Food and Drug Administration.